This key is made by combining a Crystal triskelion fragment 1, Crystal triskelion fragment 2 and Crystal triskelion fragment 3. You can use the locate option to lead you to a Rock face found just southeast of the Golden Apple Tree and Divination colony in the Fremennik Province. Once there, you can use the key to open the Rock face and receive your reward. The rewards include seeds, herbs, ores, charms, dragon equipment, gems, clue scrolls, Ancient effigies, and Dragonstone armor.